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PET met is a polyester film metallized with aluminum powder. Polyester film (short: PET film) is already characterized by high strength and surface hardness. Especially with regard to the diffusion density however, the favorable properties can be improved through the use of aluminum powder.
A PET film metallized with aluminum powder has advantages and disadvantages compared to conventional aluminum foils. The advantages of PET met are in particular, a higher tensile strength and lower production costs. The possible processing speed is significantly higher than that of aluminum foil in the composite material produced by vaporizing aluminum.
This makes PET met, the metallized polyester film particularly useful for applications such as:
High, but not absolute diffusion density
With PET met, a composite material made of a wafer-thin aluminum layer and a PET film, diffusion values of less than 0.5 cm³/m²/d for oxygen and less than 0.3 g/m²/d for water vapor even at material thicknesses of 10 μm can be achieved. These values &#;&#;are already close to the measurement limits which are indicated for the identification of the absolute diffusion density.
For an absolute diffusion density, however, a classic aluminum foil or a different metal foil has to be used.
PET met combines the positive properties of aluminum and PET film.
In contrast to a laminated composite material, the aluminum coating in PET met only causes a change in the diffusion, optical and electrical properties. The favorable strength values &#;&#;and the low specific weight of the PET film however, remains practically unchanged.
The thickness of the aluminum layer in PET met is so small that the unit, Ångström, which is derived from the atomic diameter is usually used instead of a measurement in μm (micrometers).
A measurement in Ångström can therefore be regarded as a corresponding number of atoms stacked directly above one another. This of course, does not reflect the actual physical conditions, but illustrates the extremely small thickness of the metal support layer.
The typical range of aluminum layer thicknesses for a metallized PET film of about 30 Å &#; 500 Å is about 3 to 50 nm. For comparison, pure gold can be reshaped into Å of thin gold leaf. At this thickness, gold is already slightly translucent and appears green against the light.
PET met foil is always slightly transparent.
Even metallized PET film is not completely opaque. In the case of incident light, this effect cannot be seen due to the silvery reflecting surface. This effect can be varied by printing, dyeing or varnishing as well as by brushing or embossing the PET film.
The highly reflective surface of a metallized PET film can be used to create an attractive optical effect in packaging as well as a barrier against electromagnetic radiation.
Aluminum vapor-coated PET foil reflects not only visible and infrared light, but also UV radiation. The aluminum coating differs from the silver or gold coatings used for similar purposes. Compared to these metals, the degree of reflection of aluminum is largely independent of the wavelength. The minimum which is still above 85%, is slightly above 800 nm in the near infrared range.
The reflection factor and the optical density of metallized PET film increases proportionally with the thickness of the aluminum coating. The optical density (OD) measured as the logarithm of the incident optical radiation divided by the radiation energy transmitted is typically between 0.25 and 3.5 for PET met.
The thicker the aluminum layer, the higher the optical density and the lower the transparency.
The degree of reflection is thus about 66-99% because, due to the logarithmic scaling, an optical density of 0.3 corresponds to half of the transmitted radiation intensity.
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Alteration of properties due to ageingJust as it is the case with solid pure aluminum, a superficial oxidation takes place in the aluminum coated PET film. It protects the metal from further chemical conversion, both on the side exposed to air as well as the substrate side.
This self-passivation resulting from the formation of transparent aluminum oxide leads to a reduction in the optical density and the electrical conductivity, especially in the first 24 hours after the production of the metallized PET film. It must therefore be taken into account during production if customer specifications are to be observed with regard to these values.
PET met films become more transparent over time.
Since the oxide layer grows to a maximum of 3 to 4 nm irrespective of the thickness of the aluminum coating, the effect is particularly strong with thin coatings. With an approximately 10 nm thick aluminum coating, the optical density can drop from 0.2 to 0.28 within 24 hours and to about half of the original value in the long term.
Metallized PET film is suitable, for example, in packaging technology as a direct replacement for aluminum foil. For the same film thickness, PET met is characterized by a higher tensile strength and flexural rigidity such that the composite material produced by vaporization of the metal is not as wrinkled as aluminum foil.
PETmet als Ersatz für Alu mit Vor- und Nachteilen.
This can give the package a more presentable look. Despite this, individual packages for candies, which are closed by twisting the film ends (twist closure) are also possible with metallized PET film.
However, aluminum foil also has advantages in certain packaging because, unlike PET met film, it is opaque and guarantees an absolute diffusion density. In general, food packaged with PET met film is therefore not as durable as those packaged with aluminum foil. PET met film is therefore more suitable for foodstuffs with short shelf life, which only stay in the supermarket for a relatively short time before a buyer gets it.
Further application possibilities for metallized PET film in the field of food packaging result from the fact that the extremely fine metal coating changes the electrical conductivity at the surface of the film. This makes PET met visible in metal detectors, but can also be used, for example in the packaging of microwave dishes with low water content, so that the food can absorb more energy and heat up quickly.
In the case of building insulation, the positive influence of the aluminum vaporization on the diffusion resistance as well as on the reflection of thermal radiation is important. Compared with aluminum foil, PET met offers no absolute vapor barrier, but a significantly higher mechanical resistance and a better reflectivity.
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The world has changed and the concern for the environment and the well-being of consumers is the priority. You can no longer ignore what will be done with post-consumer packaging or the possible impact raw materials´production may have on the environment. The consumer and the packaging value chain are fully aware of the importance of their roles in this new scenario. Therefore, the development of new technologies involves the evaluation of the environmental impacts of new packaging and its materials, both in the production process and after the produt´s use.
Some countries have already replaced traditional aluminum-laminated packaging by metallized flexible plastic packaging. Substitution is more concentrated in some product categories such as tomato based products, powdered milk and coffee. For instance, in Brazil almost 100% of SUP (stand up pouch) packages for tomato products, are already produced with high barrier metallized polyester films.
And this migration trend from aluminum laminate to metallized films continues globally. In fact, it follows a quite strong trend: the substitution of rigid packages for flexible packaging, especially for pouches. The advantages are many. From a simplified production process to logistics optimization &#; the benefits include reduction of packaging weight, possibility of better filling the space during transport and storage, flexibility of formats and opening / reclosing systems, etc.
It is also necessary to consider the technological advantage inherent to the flexible packaging system: it is very easy to change the packaging size or format. The flexibility of the system guarantees a greater speed of reaction to new market requirements.
There is also another advantage that &#;talks&#; directly to the consumer's pocket: flexible packaging tends to be more economical than rigid, with the same, and sometimes even better, barrier properties. This is an attribute that is being watched with great interest by several market sectors, especially by the pharmaceutical and food industries.
In addition to lower cost, flexible packaging and its production process is totally safe to the product, another positive point for pharmaceuticals and similar products. The food industry is also attracted by the food safety guaranteed by the metallized flexible package. All this is topped off by a cheaper purchase at the point of sale.
Regarding environmental benefits, a study conducted by the Flexible Packaging Association ("FPA") in the US, shows that pouches have a smaller carbon footprint. For example, the production of a 230g pouch for beverages consumes between 0.54 and 2.90 mega joules less energy compared to a rigid package - glass or plastic - with the same capacity. The studies also show that the CO2 emission is lower during the production process of a pouch versus other types of packaging.
Empty pouches are also lighter and less bulky in transport, taking up less space. There is a 26:1 ratio in the transport of empty glass on trucks compared to empty pouches for packages with the same capacity. In recent years, the replacement of rigid by flexible has been very visible in Brazil in cleaning and personal care products. The FPA study further provides evidence that pouches have a more efficient product to packaging rate and occupy less space in landfills than other types of packaging.
Metallized polyester films provide excellent barrier to moisture and oxygen. This barrier is verified by tests done before the film leaves the Terphane plants. All Terphane metallized polyester films are thoroughly tested on the line. Aluminum laminated packaging can present flex cracking and pin holes, while this effect is minimized in metallized film; it is also less susceptible to breakage during handling. To ensure total safety, Terphane uses state-of-the-art inspection technology during the metallization process.
In fact, today Terphane has a whole range of solutions that serve the industry to replace aluminum packaging. There are several processes and products that range from the simplest appearance requirements to the highest barrier with full functionality.
The bottom line is that pouches with metallized polyester films offer several competitive advantages for brand owners. In addition, metallized film is lighter than the aluminum packaging and allows more packaging units per square meters. With the advancement of production technologies and materials, the value proposition of metallized films only increases, with the benefits of shelf-ready appearance, shelf life and logistic and environmental advantages.
Each innovation that emerges contributes to accelerating the growth of the flexible packaging. On a global scale, only the pouch market has grown at a rate of 6.2% per year in recent years. Fredonia forecasts the segment will achieve US$ 37.5 billion globally by the end of this year. If we consider only the US, the annual growth rate has been 4.6%, and the expected revenue for is US$ 9.4 billion.
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